Get a large sauté pan very hot over high heat on the stovetop. Add oil and wait until it begins to smoke. Add mushrooms and toss to coat in oil. Cook for five minutes over high heat, stirring to get even color on them. Add onions, garlic and salt and cook for another 30 seconds; remove from heat and stir in butter and thyme. Serve over your favorite medium: polenta, pasta or eggs.